Xqatlnfi or plastic



106. cowosmoss,

' I COATlNGpQRPLASTlC I bKUhb KH'ILKIZNUZ txam S iPatented Nov. 7, 1944 i o: I

Joseph John Etridge, Norton-on-Tees, John 1 Briscoe Sandford, Saltburn, and Victor Lefebure, London, England, assignors to Imperial Chemical Industries Limited, a. corporation of g I Great Britain p No Drawing. Application September'29, 1941, Serial No. 412,896. In Great Britain February 9Claims. (Cl.15 445.9l (ltl I (Granted under the provisions of sec. 14, act r MarchZ, 1927;357 0. G. 5) [fir/l X This invention relates to the manufacture of ordinary cements and yet which has such an composite wallboard or plaster board consisting early set that it can be used for the fabrication of a core of a cementitious material bonded to of wallboard on a fast continuous machine of the covers of pulp board, cardboard, paper or the like, type well known in the art. It is a further object generally referred to as liners. This applica- '5' of the invention to provide a wallboard which tion is a continuation-in-part of our application can be used outside exposed to atmosphere. e, Serial No. 257,821. We have found that certain core compositions .5 In plaster board the cementitious material as herein set forth andcomprising mixtures of most generally used for "he core is plaster of plaster of Paris and groundwto Paris; catalysed anhydrite plaster sham 5655; H) w ich has been added a minor proportion of of plaster of Parisstatementscan als exciter such as ground Portland cement clinker, befisedfsetpiastefer"'Paris"sufiers from the can be bonded to paper t ive a und t o defects that it does not possess good resistance to board, and t y 68-11 be made to Set 51131- the eiiect of moisture in the form of humid air, ciently quickly to render them 4 of being it is readily softened by water, it has a high water l6 used on a fast continuous board maclnne.- Part absorbing capacity, low resistance to water ero- 0f the plaster of Paris y be replaced y sion and very low strength when saturated with hydrite or gyps m, but n ally the only water. Hence boards made with a plaster of 0111111 Sulphate Constituent will be Plaster Paris core whilst giving excellent performance Paris h o pe y um ad ed as an 32; when used in dry situations, such as within buildcolerator, for-the e set core h s eatly ings, cannot be used in outside positions where improved resistance towards moisture and damp they would be exposed 'to the effect of weather o di io s o p w p e f Paris, and particularly of water. On the other hand and in these respects has Properties aprflaching ordinary cements such as Portland, Portland tho e o Po t a d c e tblast furnace slag cement, or alumifious Ezfiieiit'sf The plaster of Paris should be prepared from "wh'ilst'all possessin'g'eiicllent resistance toaster rock gypsum and in any case must be free from and being suitable for use outside do not bond phosphates because these prevent the desired to paper and cannot therefore be used as the core reaction Etween the plaster of Paris and the for wallboards. Furthermore it is one of the blast furnace slag. We have not found plaster great advantages of the use of plaster of Paris of Paris made fromb -product sumto be suitas the core constituent that; owing to its quick aBle for our compositions. The blast furnace slag f setting properties, boards made from it can be will generally have the following composition:

produced on fast continuous machines and that the length of conveyor belt between the fabri- Per cent by 22; (3'

eating rolls and the board cutting device and qao 2 therefore the size of the plant can be kept to a S102 25"50 minimum. On the other hand all of the above A1203 types of cement set so slowly and take so long The per cent of SiOz preferably is less than to attain a degree of set suitable for cutting that 40%. The blast furnace slag and the Portland they could not be used to fabricate board on one cement should be extremely finelyground in order g. of these fast continuous machines. that the secondary reaction between the ample; It is the object of this invention to produce a aluminatesand the calcium sulphate may prowallboard with a core possessing almost as good ceed to completion. We have found that if the resistance to the effect of moisture and water as sl a clink r are ground so that by w i ht W o a.

drite' or gypsum 'ormixtures of these. Anhydrite of the particles are less than 30 microns, and if the fineness of the final mixed composition is the same as this, good results are obtained. As will be described later there are other reasons for grinding the slag and cement to this degree of 6 fineness. The maximum proportion of slag that may be used is 60%. We have found that with higher proportions of slag than this the bond between the core and the liners is defective and the boards are consequently unsound, that it is not 10 possible to obtain sufliciently early cutting set to make possible.the useof the composition on a fast continuous machine, and, furthermore, that the set cores crack and disintegrate on repeated exposure to wetting and drying. The last men- 15.. tioned defect is apparently due to expansion resulting from a further secondary reaction. IBelow 60% slag these defects are not found. On the other hand we have foimd that below 40% slag the resistance to the effect. of moisture and wetting falls off very considerably. We therefore limit ourselves to the range of compositions.

Partsbysrezght Plaster of Parls 40-60 Blast furnace slag -40 Exciter 1-45 'Iheggciter may be Portland cement, ground Portland cement clinker or any equ valentlime-con; taining or ime-producing material. That is, 80

e exc mprises ime in such cm or condition as 'to be availab e or promoting the desired reaction-between the calcium' sulphate and the blast furnace slag; and the expression available lime as employed in the appended claims is to be understood as having'such-significance. Part ofthe plaster of Paris may replaced by anhyappearssom imesto promote the efficiency of th secondary action: this may be connected with minor differences in the blast furnace slag, which of course is fairly variable in composition. The gypsum as will be described lateris chiefly added to promote the first set of the'material.

We have also found that successful results can only be achieved ifdue regard is paid to the proportion of core adhesive employed, as indicated below. It is well known in the manufacture of gypsum wallboa'rd that the bonding of plaster of Paris to the liners is not sufliciently good to give a commercially'sound'strong board and consequently adhesive materials such as sgluble natural g s, e; g., gum ara ic; k'araya gum, exr W I- r nes, dextrinate s arc es, sta'rc es, urea and 50 m wmch the bare core thiourea formaldehyde szruE and the must ded to the core mixto promote this-bond. 'Ihe'amount of these materials that maybe thus nsed'in wallboard of'the'prior artmay vary between 0.5 and 5%, e: g., 2% dextrine and 2 /z% urea formaldehyde syrup are suitable quantities, and it is common practice to increase the quantityof adhesive ifTor any reason poor bond is obtainedonthe plant. We have found that the kindand proportion of adhesive that can be used with our novel compositions are critical, and particularly that the addition of all types of-soluble or water dispersible organic. materials markedly affectsthe strength of the set core. We have further found that, whilst up to 1% 7 or organic modifier produces some falling oil, the strength ls sufliclently goodLto give acommeroially good board. Beyond 1%, however, the 10$ iii-strength is'so great that theboards are useless. We havefozmdthat' additions of urea 15 formaldeh de s rup do not give good bond with the compositions of the invention and they should not be used with them.

These points are illustrated in the tables.

Table 1 shows the benefit of the greatly improved resistance to moisture of these compositions as compared with ordinary plaster of Paris. In a composite material such as plasterboard, which consists of a cementitious core reinforced by paper liners, the tensile stress in bending is taken by the bottom liner, which functions similarly to steel. in reinforced concrete,v and the compressive stress is taken by "the core.

The compressive strength of a normal set plasterboard core mix and that of our set new composition were compared. 2%" standard compression cubes were made from the core mixes shown, which are as they would be used in plasterboard, and they were allowed to mature in humid air. for two days and were then dried toconstant weight at C. One set of cubes was testedfor. compressive strength one hour after drying. The other set was exposed for 30 dayszin'a-humidity cabinet and was then tested as'before.

Table 1 Compressive strength, lb./sq. in. Composition of mix, parts by weight As Afterlmonth made 33%??? 23 ucoo Portland cement r 3 4'295 @638 Water 31 In Table 2 the manner in which core bond varies with composition is brought out. Core bond is assessed by taking a sample of board about 6" square and attempting to strip off the 4,.) liner parallelto the grain. With firstclass bond it is impossible to strip the liner from the core, the paper always tearing, trary adhesion value of 6 is allocated. With very poor adhesion the liner can be easily stripped from the core and leaves no paper fibre adhering to the latter; the arbitrary value of 0 (zero) is allocated. Intermediate degrees of adhesion are allocated numbers between 0 and 10. A value of 8 corresponds to a degree of adhesion is exposed to a distance of about a: inch when the liner is stripped. This is the lowest value that is acceptable in first class board, although an adhesion value of 7 may be tolerated as the absolute limit in exceptional circumstances. On testing in this way an adhesion value of 7 permitsthe liner to be detached from the core over an area of which the depth is from r: tor; inch: an adhesion value of 6 similarly corresponds to stripping over a depth Dire-A inch. It is evident from the table that in compositions containing more than 70% slag the bond cannot be relied upon. The critical proportion of slag is about-65%;and the present invention is limited to proportions less than this. However, in order to provide a safety factor in the obtaining of consistently reliable adhesion in large scale manufacture we prefer to use proportions of less than 60%. As already mentioned above there are further reasons for selecting this upperlimit.

itself, and an arbir I iUb. bum UOIHUIU, uuuuu Eh buiwbuvno I t-Au'uu aseaoeo 3 Table 2;

Adhesion value of core from following mixes Stucco 50 Stucco 40 30 Exciter 3 Exciter 3 Exciter 3. Exciter 3 Core adhesive ciUter 2 filter 2 flter 2 dAfter 2 A ays ex- As ys ex- As ays ex- As ays exto to us. to os. to mm than inid umid umid all air air air dextrine l 8 9 8-7 9 8 3 urea formaldehyde syrup containing 7 50% so ds 7 3 4 0 0 0 0 5% urea formaldehyde syrup containing 50% solids 6 9 6 0 0 0 A further advantage secured according to this quick setting and hardening. Rapid hardening invention is freedom from cracking. Composiis essential for good cutting. Table 4 indicates tions containing more than 0% slag tend to 0 that as the proportion of S increases beyond crack in after life owing to further reaction, and 70% the compositions become p gressive y the critical proportion of slag is again about 65%. slower setting and hence cannot be used at the This Table 2 also shows that urea formaldesame high rates of output; With higher slag conhyde syrups are not satisfactory for use as core tents a proportionately higher quantity of exadhesives in core mixtures which include blast 33 citer is necessary. This is a further reason w y furnace slag in accordance with the present inwe prefer mixes containing not more than 60% vention. slag. The rate of hardening is measured by The effect of organic modifiers used to improve means of a small punch of the Brinell type and core adhesion upon the transverse strength of the hardness is assessed qualitatively by the dithe set core mix is given in Table 3 and from ameter of the depression produced; the smaller this it-will be seen that the use of greater quanthis is, the harder the material. Practical extities than 1% of these materials causes serious perience shows that core compositions cannot be falling or! in strength. The water quantities satisfactorily out if the diameter of the depresgiven are those to give the consistency required sion is greater than 7.5 mms.

Table 3 Transverse strength (1b.) of Adhesite 4" x 1" x 1" prisms tested Water per at 3 centres Composition of mix cent on composition Type gggg gg 1 day 3 days 7 days,

(is; 60 4 40 100 143 143 Stucco 40 32.5 10 120 130 Portland cement 4 32.5 43

. s2 s1 57 75 4o 65 115 130 62 3o 10 on the plasterboard machine. 4" x 1" x 1" Even with the mixes containing -60% slag prisms were prepared and matured in humid air the setting time tends to be rather longer than until they were tested. than required for the range of plant speeds nec- Table 4 Exciter water zggg gf Diameter of depression (mms.) at times given (mins.) Composition of core (Portland quantity cement) per cent 7 Mins. Secs. 1 s 9 1o 11 12 13 i4 15 19 :4 4s 5 1o 4 4s 4 15 5 4s a so a 49 4 so 4 4o 4 o 5 4o 5 o 2 49 4 2o 3 49 4 15 4 49 4 4o 2 so a as I a so 2 I 4 so a 10 Q As already mentioned, it is an important feaessary to the righ rate of output of modern ma ture of our invention that the new compositions chines. This appears to be partly due to the efcan be employed on normal continuous plasterfect of the alkaline materials in the exciter and board machines 'because they are sufilcientiy 7 may also be influenced by variation in the slag.

- In carrying out the We have found that these difliculties can be overcome by employing warm mixing water and by adding up to of groun se p as er card core calculated on the weig o e ry composi ion. The water maybe heat? to -7019, but we prefer the range 30-50 as e control of mixing is much better. Table 5 shows the benefits that may be obtained in this way using 60 slag/ stucco Similar benefits are obtained with the mixes containing more stucco than this.

- Boards of commercially acceptable standard can be produced from the compositions by the methods we have already described. However, with the use of the compositions in this manner occasional variations in bonding properties'may be met with due to variations in the composition of the slag, and it is not permissible to meet this difliculty in culty is met in plaster of Paris boards, namely, by increasing the quantity of adhesive since such increase would seriously reduce the strength of the boards as above described. Moreover the presence of added adhesive in the cores of the present invention tends to reduce the compressive strength of the core. We have found a method of removing these difiiculties which consists in eliminating the adhesive from'the core mix and applying a special coating to the liner. This method, which possesses the combined advantages that the full strength of the set core is developed and that owing to the elimination of the core adhesive development of initial adhesion between paper and core mix and rate of set are greatly improved, consists in the application, to. the specific core mixes of the present invention,"

of the invention described and claimed in pending appl cation No.

' aspect of the present invention we apply a coating of the following composi tion to the liners before they contact with the wet plastic mix used in the present invention as the plaster board core.

Stucco or plaster of Paris The preferred proportions of water lie between 60 and 150 parts by weight. The agl he siye is a water soluble. one selected from the class,

soluble s, e. g.,-arabic, kara a, or tragaganth, water soluae dextrin s, and starches. I The amount of water and the amount of re-.- tarder employed depend upon the method of application used, for example whether spray, roller, brush, doctor or trough. The coating is applied in a thickness of from 0.0005 and 0.05 inch, but we have found that the preferred thickness for reasons of efiiciency and permanence of bond, rate of development of bond, and cost, lies between 0.0005 and 0.005 inch. We have found that thecore mix may be applied to the coated liner the way in which the analogous difliwhilst the surface of the coating is in the liquid condition or after it has dried. We find that the --best results in the before-mentioned respects are 215,922 and its continuations.

" lows:

' Portland cemenalI:LIIIIIII:

obtained if the coating is in the unset liquid condition and if it has reached the tacky stage by evaporation of water into the air and absorption into the liner. It is essential that the liquid coating should not become dry before contact with the core mix else the bond will be very poor: it is also essential that a large proportion of gypsum should not have formed in the coating before it contacts with a plaster mix. It will be appreciated that the above conditions can be attained in many ways. We find that the optimum conditions are attained by using a coating'mix containing from 50 to 600 parts of water, varied to suit the application means, and retarded so that 13 minutes afterv mixing the amount of combined water in the plaster has not risen by more't'han 2%. Or anic scutch retarders or phosphate retarders composed'o mix ure's" of so rurii'hxa metaho are suitable. coa

ing mixes of the above type the tacky stage is achieved. Furthermore it'is desirable that a mix having -a life of 13 minutes measured as de scribed above should not be used after it has attained a life of 11 minutes. 1

Whilst we have given the above description Ofthe preferred method of carrying out our invention,. and the conditions we find to be necessary,'we wish to make it clear that any variations in waterquantity, retarder quantity, life of mix, time of application, which give conditions equivalent to those'we have described come within the scope of this feature of our invention.

We have also stated that the coating may be used dry.- We use the qr sthod and indicate its limitations as follows. e wa er quantity will not be less than calculated on the stucco, and will lie preferably between and-600%. The amount of coating should be reduced to a minimum on account .of the danger of the dry coating cracking and flaking off: we prefer to use thicknesses of 0.0005 to 0.005 inch and weights of up to 0.25 lb. of liquid coating per sq. yard of liner. The coating'is dried by passing the liner over a heated roll 15 to 90 seconds after applying the coating. The roll should be maintained at a temperature of to C. and the time of contact should be about 40 seconds.

Example 1 A plaster board core mix was employed as fol- Parts by weight Finely ground blast furnace slag 50 Plaster of Paris 50 At least 60% of the mixed cement was of diameter not exceeding 30 microns, i. e., 60% of flour.

The mix was gauged with 48% i an initial set of about 9 minutes and a in set of about 20 minutes. A normal plaster board liner of high jute content, of thickness .03 inch, was employed and plasterboard was formed in the usual'way from such core mix and such liner. The board after forming and cutting was'transferred to the drier where it was dried at-70 C. On testing for adhesion after manufacture the of water giving 106. CUMFUSI l was,

humid atmosphere.

' As regards core adhesive, various types are possible, but gumarabic was used, in two concentrations, i. e., tively.- The adhesion in this wet, was '10. Y

As regards quicker setting mixes, the above core mix was accelerated um givin'g'an mitial minutes and a %a1 set of 10 minutes, the

erator set of 5 board produced be i. e., ground a and 1% on the mix respeccase, both dry and with a standard acceling perfectly normal as above.

Example If A plasterboard was made from the following core mix employing gauging water at 50 Parts by weight bKUbb KEY Ell Elbl:

The particle size of core was the same as in Example 1. 2% ground plasterboard gore was added in the mixer as acce crater 'I'firs' fiiiii'was applied to liners which had been precoated with roll at 140-180 C., the time of contact being 40 seconds, and then stored.

Parts by weight Phosphate stucco 1 l0 Dextrine Scutch retarder 0.04 Water Y 1oo Initial adhesion develops in 12 minutes, and the board can be cut at 13 minutes. The final core adhesion value was 8, and fell to 8-7 after 48 hours exposure to' saturated air. Unsatisfactory final core adhesion and very long delay in the development of initial adhesion were obtained when this core mix was used without the Slag 0 29 positive bond coating and with 1 per cent. of

Stucco 40 dextrine as core adhesive. Portland cement clinker 3 We have found that plaster boards made by Dextrine 1 this process can be dried at those temperatures Sawdust 4 normally used in the in dustry when the normal Water '45 core of plaster of Paris alone or with fillers is em- The particle size of this core was the same as in Example 1. 5 parts by weight of ound plaster; board core was introduced into tie mixer. The

wet mix was applied to wallboard liner. boards set quickly and attained cutting set at 6 /2 minutes.

Without the addition of the boards would not have attained 18 minutes. the temperature of the gauging water was 20 C.

When the The They were dried at a temperature of r tor the cutting set before su was omitted and the cutting interval was 24 minutes.

Example 3 A plasterboard was made from the following core mix employing water at 50 C.

Parts by weight 60 The particle size of this as in Example 1. 2% ground I A was added in the mixer as accelerator." This'mix core mix was the same plasterboard core was applied to liners which had been coated 20 seconds before with 0.2 lb. per square yard of a coating having the following composition. \h .p

" Parts by weight Phosphate stucco 100 Dextrine 5 Scutch retarder 0.04

Water 65 Initial adhesion developed in 9 minutes and the board could be cut at 10 minutes. The final core adhesion value was 9 and only fell to 8 after 48 hours exposure to saturated air.

Example 4 A plasterboard was made from the following core mix employing water at 50 C.

Parts by weight Slag 60 Stucco I 40 Portland cement clinker 3 Sawdust 4 Water 45 ployed. Such temperatures are as follows. The

inlet temperature of the ,ririer..is.-130?.300f'.,..

preferably 130-l50 C., and the outlet temperature may be 70-l30 C. and is preferably 100"- 125 C. When the new board is made by such normal drying, we have found that the strengths of such board are similar to those of normal plaster board, i. e., not effectively higher. But we have found that by drying at lower temperatures, preferably in a range between 50 and 70 C. stronger boards are obtained, chiefly because the normal hydration and strength development of the core is not arrested but encouraged. Of

course, temperatures below 50 C. will produce strong dried boards, but at such temperatures the drying efi'iciency is reduced.

Plaster board made according to the invention is characterised by high mechanical strength and resistance to water and corrosive substances found in the atmospheres of large towns. Ac-

- cordingly it is suitable for external building work.

Actually the strength of the core increases rather than decreases under constant wetting. In this respect the core resembles Portland cement, but unlike Portland cement it is not markedly alkaline and consequently has no harmful effect upon the fibre liner or on any decoration superimposed thereon,

If a light weight or cellular core is desired, foam containing mixes may be used in the same way as in making plaster of Paris board.

As many apparently widely diiferent embodiments of this invention may be made without departing from the spirit and scope thereof, it is to be understood that the invention is not limited to the specific embodiments thereof except as defined in the appended claims.

We claim:

1. A composite board comprising a layer of set water setting cement bonded on both sides to liners of fibrous material, said cement comprising between 40 and 60 parts by weight of calcium sulphate, between 60 and 40 parts by weight of blast furnace slag, and between 1 and 15 parts {3y weight of an exciter comprising available ime.

2. A composite board comprising a layer of set water-setting cement bonded on both sides to 75 liners of fibrous material, said cement compris- Examin the following mix, dried by passage over a hot i least 60 per cent. by: weight of, the particleeare less than 30 microns, and between 1 and 15 par ts by weight of an exciter comprising available lime, at least 60 per cent. by weight of the of the exciter being less than 30 microns.

3. A. composite board as claimed in claim 1, in which the cementitious material is free framed hesive.

4. A composite boardas claimed in which the cementitious material'contains a proportion of 'adhesivenoh greater than 1 per cent.

trin

5. Acomposite board'asslaimed in-c1aim1, in which theexciter is Portland 1 cement clinker.

particles claim 1, in-

byweight, said adhesivebeingiselected from-the group v consisting:- of gum-arabic, starch-andflexgaqggaq,

ing aset containing between 40 andififlflpartsr by weight of calcium sulphate, between 60 andAO'. parts by weight of blast furnace slag of. which at;v

6. A composite bowing-claimed imclaim 1, .In; which, at, least a. noriian ,oLthealcium sulp ate constituent. of the cement, consists, of, calcium sulphate hemihydrate.

7. A composite aardz firfllfiimed in c aiml in which avfoem-containing mix. is,employed.

8. A.composite board asy la-imedinlclaimi inwhichthemix contains a malllnroportionzoi finely-divided gypsum, e. g., ground semnlaster 0!, Paris:

Acommsite nrdasd l imedi nsla mlliin which, a11 of the calci m, sulphate, constituent 0L the cement, consistsi of calciumculnha te hung-i hy rat JOSEPH JOHN ETRIDGE. JOHNBRISOOE SANDFORD. 

